1. Field of the Invention
The present invention relates generally to a disconnect check valve mechanism that is applicable for releasable connection with a wide variety of payloads such as direct circulating flow valves, reverse circulating flow valves, formation fracturing tools and the like. More specifically, the present invention concerns a disconnect check valve mechanism that is connected to a payload, run into a well, and operated in a reverse circulating flow condition until its disconnect is actuated, leaving the payload within the well and permitting retrieval of the disconnect check valve mechanism with its check valve or valves enabled, thus permitting only direct circulating flow and preventing the inflow of wellbore fluids into the tubing string.
2. Description of Related Art
It is a safety standard in coiled tubing operations, to have a check valve assembly with a minimum of two pressure barriers in the tool string. In many coiled tubing operations, such as fracturing and well cleanout operations, it is desirable to reverse circulate through the coiled tubing. Reverse circulating (flowing upwardly within the passage of the coiled tubing instead of downwardly) is not possible when a conventional direct circulating dual check valve mechanism is employed.
It is a principal feature of the present invention to provide a novel tubing supported disconnect check valve mechanism or tool that functions as a passive selectively operated disconnect apparatus to which a variety of well servicing tools or payloads may be connected for use in a variety of well servicing applications.
It is also a feature of the present invention to provide a novel tubing supported disconnect check valve mechanism that can be selectively disconnected from the payload to which it is connected, and retrieved from the well with its check valve or valves in the retrieved portion thereof enabled, thus permitting direct circulating flow only while preventing the inflow of wellbore fluids into the tubing.
It is another feature of the present invention to provide a novel tubing supported disconnect check valve mechanism that accommodates industry safety standards when the tubing being utilized within the well is coiled tubing, so that downhole check valve barriers are provided during retrieval to prevent the inflow of wellbore fluids into the tubing.
Briefly, the various objects and features of the present invention are realized by providing a tubing supported disconnect check valve mechanism that is run into a wellbore connected with a payload in the form of a well servicing tool (which may be as simple as a ported bullnose), and with its check valve disabled by a mandrel within the disconnect check valve mechanism which is normally maintained at a check valve disabling position and is selectively released from its retained position and moved to a check valve enabling position. The disconnect check valve mechanism is normally passive within the tool until such time as disconnect and retrieval becomes desirable or necessary. For retrieval of the disconnect check valve mechanism, the internal mandrel is actuated to its valve enabling position, thus enabling the check valve or valves to prevent reverse circulating flow and the inflow of wellbore fluids while permitting direct circulating flow. The internal mandrel can be actuated to its valve enabling position by a drop ball and tubing pressure, by tension, by pressure differential, or by any other suitable means, and is retrieved along with the disconnect check valve mechanism after separation of the disconnect check valve mechanism from the payload tool. The housing of the payload or well servicing tool defines an internal pulling profile, thus permitting its retrieval by a fishing tool, spear, overshot, or any other type of retrieving tool.
After a well servicing operation has been completed, assuming the payload well servicing tool is to be retrieved from the well, as is typically the case, a tension force is applied to the housing of the disconnect check valve mechanism via the tubing string, thus moving the disconnect check valve mechanism and its connected payload upwardly within the well to the surface. The disconnect check valve mechanism will have remained passive during tool running, servicing operations, and during retrieval. In the event the payload well servicing tool should become stuck within the well, or if another condition should occur that makes it desirable to disconnect the disconnect check valve mechanism from the well servicing tool, the disconnect mechanism can be actuated to disconnect from the payload and to enable the check valve or valves for direct circulating flow only and prevention of the inflow of wellbore fluids. When the disconnect check valve mechanism is designed for drop ball and tubing pressure actuation, a closure ball is dropped or pumped through the tubing string to the disconnect check valve mechanism and blocks the flow passage of the internal tubular member or mandrel and, with the mandrel, defines a pressure responsive surface area or piston area. Disconnect actuation pressure is applied via the tubing string to act on the piston area and develop sufficient force to shear retainer pins or otherwise release the inner tubular member or mandrel from its check valve disabling position and shift the mandrel to its check valve enabling position. The inner tubular member or mandrel will then remain at this check valve enabling position within the tubular housing, thus causing the check valve mechanism to remain in its direct circulating flow mode. The mandrel moves down when the closure ball is dropped and the tubing pressured-up, but then comes out of the well with the check valves. This leaves the bore of the payload well servicing tool open and free to receive internal fishing tools after disconnecting.